To obtain F.sub.1 hybrid seeds, which have many advantages over non-hybrid seeds, seed breeders cross-pollinate carefully selected parent plants. In the case of plants, for example small grain cereal plants, which have hermaphroditic flowers and normally self-pollinate, this is achieved by removing the male anthers from each of the flowers by hand, an operation which is extremely time consuming and requires highly-skilled workers. Much research is being carried out into treatments with chemicals by which this same result can be achieved without the necessity for such hand-operations.